fix(model-fallback): align OpenAI fallback resolution across CLI and runtime

Keep install-time and runtime model tables in sync, stop OpenAI-only misrouting when OpenCode Go is present, and add valid OpenAI fallbacks for atlas, metis, and sisyphus-junior.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/shared/model-requirements.ts

@@ -121,6 +121,11 @@ export const AGENT_MODEL_REQUIREMENTS: Record<string, ModelRequirement> = {
         model: "claude-opus-4-6",
         variant: "max",
       },
+      {
+        providers: ["openai", "github-copilot", "opencode"],
+        model: "gpt-5.4",
+        variant: "high",
+      },
       { providers: ["opencode-go"], model: "glm-5" },
       { providers: ["kimi-for-coding"], model: "k2p5" },
     ],
@@ -149,12 +154,22 @@ export const AGENT_MODEL_REQUIREMENTS: Record<string, ModelRequirement> = {
     fallbackChain: [
       { providers: ["anthropic", "github-copilot", "opencode"], model: "claude-sonnet-4-6" },
       { providers: ["opencode-go"], model: "kimi-k2.5" },
+      {
+        providers: ["openai", "github-copilot", "opencode"],
+        model: "gpt-5.4",
+        variant: "medium",
+      },
     ],
   },
   "sisyphus-junior": {
     fallbackChain: [
       { providers: ["anthropic", "github-copilot", "opencode"], model: "claude-sonnet-4-6" },
       { providers: ["opencode-go"], model: "kimi-k2.5" },
+      {
+        providers: ["openai", "github-copilot", "opencode"],
+        model: "gpt-5.4",
+        variant: "medium",
+      },
       { providers: ["opencode"], model: "big-pickle" },
     ],
   },